If you attempt to change drop-down list options dynamically on the client side you may have issues with postback as the drop-down options will not match what the server originally sent to the client. One way to overcome this is to have a server control with all the possible values (that is hidden on the UI) and a visible client side only drop-down list that is dynamically changed. As the client side drop-down values are changed keep the server side control synchronized and then use the server side control value on post-back. Simple sample below: